This invention relates to heat exchangers, and more particularly to heat exchangers formed by a pair of concentrically spaced tubes defining a substantially annular chamber therebetween and bearing an internal metallic fin in the form of a strip of corrugated sheet metal extending spirally within the annular chamber and bridging the space between the tubes.
Heat exchangers of this type have been employed for some time within the refrigeration field, automotive field and the like for providing a very effective heat exchange between fluids confined within the tubes and fluid externally thereof. One such heat exchanger is shown in U.S. Pat. No. 3,197,975 issued Aug. 3, 1965, to Cecil Boling and assigned to the common assignee. In that patent, a very effective heat exchange unit is formed by a plurality of substantially horizontal tube assemblies each extending generally parallel to each other and formed by a pair of concentrically positioned tubes defining a substantially annular chamber therebetween which is connected at its opposite ends for the flow of the heat exchange fluids therethrough while the other of the heat exchange fluids is carried by the internal of the two concentric tubes. Each of the heat exchange tube assemblies bears an internal metallic fin assembly within the chamber which is formed of a strip of corrugated sheet metal extending spirally within the annular chamber with each of the corrugations being substantially straight and non-distortable and extending longitudinally of the chamber and bridging the space between the tubes and being pressed into contact with respect thereto to thereby divide the annular chamber into a plurality of substantially parallel longitudinal passageways, each extending between the side edges of the strip of corrugated sheet metal. The adjacent turns of the spirally formed strip of corrugated sheet metal are spaced from each other to provide a spiral passageway between the side edges of the adjacent turns to reduce the effective length of each of the longitudinal passageways to that of a single corrugation of the strip and to permit arcuate fluid flow of the heat exchange fluid confined between the tubes, between the serially-related longitudinal passageways along the annular chamber. The distance between the tubes is such that the inner and outer peripheries of the fin assembly have radial compression forces exerted upon them such that the corrugations are placed under radial compression and are subjected to sufficient force to insure a good heat-transfer relationship between each of the tubes in the internal fin assembly.
While this concentric tube heat exchange assembly provides a highly effective and efficient heat exchange between the heat exchange fluid internal of the inner tube and that confined between the tubes or between a fluid confined between the two tubes and a fluid external of the outer tube, it has been determined that the heat transfer coefficient and particularly the boiling heat transfer coefficient can be improved by improving the heat exchanger characteristics of the internal metallic fin of corrugated sheet metal strip.